Glycosidation route to 4"-epi-methylamino-4"-deoxyavermectin B1

Abstract

A stereocontrolled glycosidation with thiophenyl 4-(N-allyloxycarbonyl)-epi-methylamino-4-deoxyoleandrose and 5-O-allyloxycarbonyl avermectin B 1 monosaccharide using N-iodosuccinimide produces exclusively the α-anomer of a precursor of 4"-epi-methylamino-4"-deoxyavermectin B 1 in 90% yield. Deprotection and crystallization as the benzoic acid salt yields 4"-epi-methylamino-4"-deoxyavermectin B 1 (emamectin benzoate), a potent insecticide.

What is claimed is: 
     
       1. A process comprising the step of reacting the compound of the following structure: ##STR7## with a compound of the following structure: ##STR8## where the combination of X and Y is either H, SPh, or SPh and H, respectively; or mixture thereof; in a polar, aprotic organic solvent, in the presence of a proton acceptor agent and an iodine-containing condensing agent selected from the group consisting of iodine or N-iodosuccinimide, at a temperature in the region of -15° to 100° C., for a sufficient time to form the compound of the following structure: ##STR9## 
     
     
       2. The process of claim 1 wherein said temperature is in the region of 15° C. to 40° C. 
     
     
       3. The process of claim 1 wherein said solvent is selected from, C 3  -C 10  linear or cyclic alkanoamides, C 2  -C 10  linear or cyclic ethers, mono, di or tri-halogenated, C 1  -C 4  alkanes, mono or di-C 1  -C 4  alkylated C 6  -C 10  aromatics. 
     
     
       4. The process of claim 1 wherein said proton acceptor agent is diisopropylethylamine, collidine, 2,6-di-t-butylpyridine or 2,6-di-t-butyl-4-methylpyridine.